I don't know if you have family nearby or could arrange for some type of trusted help for short periods now and then so that you and hubby can have some alone time.
My hubby and I have gone through this type of rough patch also-and I DON'T have TWINS, girl!! Ditto what everyone else said, you are super mom. You are really giving it your all. And part of that is the sacrifice that your hubby and you are making so you can be home with them, which is the best gift you could give to them right now. Take time to reflect on that, and you and your husband can remember to bond over the fact that you are working together to give them the best life possible. Feeling like you are working together for a common goal can keep you united.
That fact can get easily get lost in the day to day madness.
Being a mom with Cf has its big challenges, at least it has for me. Added to that fact is that my husband has a very demanding job which takes him away from us often. Thats one of the biggest stressors for us and we go through periods where there is just a divide between us.
Something we've decided to do is take time alone together whenever possible, even if its brief. For every doctor appt I have, we always have family watch our daughter, and we go to my appt alone together, and have lunch or dinner afterwards. Its usually only a couple of alone hours together but they add up.
And about every 6-9 months we do a weekend alone together. This is hard for me bc I hate leaving my LO, but I have come to see the wisdom in leaving for a few nights. We really get to reconnect and breathe for a few days.